Patent GB-578416-A (GB)
Title: Facsimile system and apparatus
IPC: H04N1/12
Filed: 1944-01-21
Abstract: 578,416. Facsimile telegraphy. CREED & CO., Ltd. Jan. 21, 1944, No. 1204. Convention date, Jan. 29, 1943. [Class 40 (iii)] The scanning element in a facsimile machine is moved back and forth and scans in both directions, the element being operated at a speed slightly in excess of synchronous speed and its position being corrected by reversing the scanning element to cause it to start each backward and /or forward stroke at an interval after the synchronizing signal. Scanning arrangements. The sheet 26, Fig. 1, to be scanned is supported on a sliding table 21 which is moved in one direction against the action of a spring drum 29 to store energy for moving the table during scanning, the releasing movement of the table being controlled by an escapement device 47, 48 which is controlled by synchronizing pulses applied to electromagnets 143 or by a balance wheel 53, Fig. 2, if the movement is a master movement. In the latter case, the oscillation of the escapement control is employed to produce synchronizing signals. The escapement wheel 47 advances through an angle equal to half the pitch of'its teeth at each movement and its spindle 42 carries a cam-wheel 43 having twice as many projections 131 as the wheel 47 has teeth, the projections 131 being arranged to move a lever 148 to allow the movement of the scanning element 74 in each direction to commence. The scanning element is driven by a motor M which operates a shaft 164 through an electromagnetic clutch 145 operated by a magnet 144. Shaft 164 carries a crank 149 which is driven through a lost-motion device 146 in which the required correction of the position of the scanning element is effected, rotation of crank 149 causing the oscillation of lever 154 which reciprocates a spring drum 159 which is connected to the scanning element 74 by a cord 92. The amplitude of movement of lever 154 can be adjusted at 162. Cord 92 is wound on the drum when element 74 is moved in one sense, and when the movement of the drum is reversed, element 74 is operated on by a cord 93 connected to a spring drum 161 to return the element. The path of movement of element 74 is at right angles to the path of movement of table 21. Synchronizing. As seen in Fig. 4, shaft 164 extends through device 146 and is provided at one end with a threaded portion 167 which is engaged by the hub 168 of a stop disc 169. At the other end, shaft 164 is also provided with a thread 186 which is twice as fast as thread 167, thread 186 being engaged by a pin 184 which projects inwardly of a cam-sleeve 183 which is carried on the shaft. Cam-sleeve 183 has a groove 182 at one end which is engaged by pins 181 in the U-shaped end of a lever 179 which is pivoted at one end of a crank-shaped member 176, the other end of which is pivotally connected to one arm of a yoke 173 which is constrained towards member 176 by a spring 175 and has a further arm connected by a link 178 to an intermediate point on lever 179. Movement of yoke 173 under the action of spring 175 is normally prevented by engagement of projections 172 on the yoke with a flange 171 on the hub 168. The other end of sleeve 183 has a flange 187 having diametrically opposed openings 188 through which rods 189 extending from a disc 191 pass. Disc 191 is free to rotate, but not to slide on shaft 164 and is rigid with the crank 149. Cam 183 has two diametrically opposed grooves 218, Fig. 9, which co-operate with a follower 213, lever 209, rock-shaft 207, and levers 206 and 199 for the actuation of a T-shaped correcting member 197 which is reciprocated in the path of diametrically opposed projections 195 and 196 on stop disc 169. Member. 197 is lifted out of the path of the projections at the appropriate times by operation of lever 148, Fig. 10. Shaft 164 tends to run faster than synchronons speed, disc 169, sleeve 183 and disc 191 rotating in unison with the shaft. While follower 213 is engaging large diameter portions of sleeve 183, member 197 is in the extreme position shown in Fig. 9. The grooves 218 are formed so that when a projection 196 or 195 engages member 197, the movement of follower 213 is such that member 197 retreats at the speed at which the projection advances till the follower reaches the bottom of the groove as shown in Fig. 10. Assuming that lever 148 is not actuated at this point to raise member 197 clear of the projection, member 197 will move to the left engaging projection 196 and rotating disc 169 backwards so that the disc moves along the threaded portion 167 of shaft 164. This movement is transmitted via the system 173, 176, 179 to sleeve 183, which is also caused to rotate backwards on the shaft due to the engagement of pin 184 in thread 186, the pitch of the thread being such that sleeve 183 moves backward with relation to the.shaft 164 so fast that member 197 is caused to move the disc 169 backward at twice the speed at which the shaft 164 rotates. When a position such as that shown in Fig. 12 is reached, member 197 will rise out of the path of projection 196 and disc 169 will be free to rotate with shaft 164, and will advance to the position from which the next scanning stroke is begun. The scanning stroke thus commences with a delay proportional to the lack of synchronization. Disc 169 continues to rotate till projection 195 is engaged by member 197. However, if the speed of shaft 164 is constant, lever 148 will be operated to raise member 197 out of the path of projection 195 before any backward movement occurs, since the projection 195 and the scanning element 74 will be in the correct position when lever 148 is operated. If the speed of shaft 164 is increasing, some correction will be applied at this time, but if shaft 164 slows down, the correction applied at earch alternate half-revolution will decrease. In no case will there be any progressive departure from synchronism as scanning proceeds. The scanning strokes of the element 74 are of such amplitude that the range of movement in which the synchronizing correction occurs is not employed for recording or transmission of signals. Transmitter and receiver circuits. Fig. 2 shows schematically the circuits for starting, stopping and synchronizing a transmitter and a receiver. In the transmitter, the scanning element comprises a light source 77, chopper 78 and photo-electric cell 79 for producing picture signals which are fed to a line 83. The scanning element in the receiver comprises a stylus 87 which is operated by received signals. To stop-operation, switch 222 at the transmitter is moved to its left-hand contact. This applies a negative voltage to line 83 and also operates relay 226 to its left-hand contact. This energizes relay 228 which closes the operating circuit for clutch magnet 144, thereby releasing transmitter clutch 145, and the operating circuit for magnet 72, the armature 68 of which is rocked to lock balance wheel 53 in the position shown so that escapement member 48 closes contacts 221. With negative potential on the line 83, the armature of relay 229 at the receiver is operated to its right-hand stop, thus energizing relay 232 which closes operating circuits for clutch magnet 144 and for the left-hand magnet 143 so that the escapement member 48 at the receiver stops in a position corresponding to that of member 48 at the transmitter. To start scanning operations, switch 222 is moved to its right-hand contact, thus energizing relay 226 to its right-hand contact and applying positive potential to the line. Relay 228 is de-energized and magnets 144 and 72 release so that the transmitter commences to operate. The positive potential on the line 83 causes relay 229 at the receiver to operate to its left-hand contact, causing relay 232 and receiver magnet 144 to release, and the receiver starts. Operation of relay 229 closes a circuit through the tongue of relay 234, one winding of relay 237, resistances 238 and 241 to a negative source, causing relay 237 to operate to complete a circuit from the junction 239 of resistances 238, 241, through resistance 243, relay winding 234, right-hand winding of relay 237, tongue of relay 237, rectifier 246 to ground. Resistances 238 and 241 are such that point 239 is normally at zero potential, while rectifier 246 prevents current flowing through relay winding 234 should point 239 become positive. When escapement member 48 at the transmitter disengages contacts 221, the positive impulse on the line ceases and relay 229 becomes inoperative. This breaks the connection to the positive source from point 239 through the left-hand winding of relay 237 and point 239 becomes negative causing a current to flow through relay 234 and the right-hand winding of relay 237 so that this relay remains operated and relay 234 is operated. The outer tongue of relay 234 applies positive potential to the right-hand magnet 143 so that the escapement member 48 at the receiver is drawn to the right to permit the advancement of the escapement wheel and scanning table by one step. When the escapement member 48 at the transmitter engages its contact 233 in its right-hand extreme position, a further positive impulse appears in line 83. The tongue of relay 229 is again operated to its left-hand contact and connects the source of positive potential through the inner tongue of relay 234 with the point 239. Thus, the current through rectifier 246 ceases and relay 234 releases so that positive potential is removed from the winding of right-hand magnet 143 and applied to the left-hand magnet, causing member 48 to swing to the left, permitting a further advancement of the scanning table and initiating the return stroke of the scanning element. Relay 237 becomes inoperative. As further positive impulses are received from line 83, the cycle of operations above described is repeated and the scanning movement of the receiver continues in synchronism with that at the transmitter until switch 222 at the transmitter is moved to its left-hand contact t